Don't know about your port requirement but do a Google search for Hsu and SVS, their original websites should give you all the details.
I'm considering the Onix Rocket ULW-10, which is sealed, front firing and costs $499. Others you might want to look at: PSB SubSonic 5i, front firing and ported to front at $449; and the Adire Audio Rava, sealed, front firing ant only $399.
I have Monitor 5's, CC370, and Mini's for the rears. My sub of preference is the Paradign PW2100. It flat out does the job. It needs some break in time but once broken in, it is outstanding for both music and movies. I haven't done alot of bragging about this sub in this forum beacuse there are alot of Onix, Hsu, and SVS fans, and although I think those are great subs I believe you have to pay considerably more than the going price for the PW2100 to outperform it. It is an all around superstar. Oh and by the way you can get it to match your Monitors as it is the recommended sub for your speakers.
The PW2100 is front firing, rear ported. Mine is about 8 inches from the rear wall.
I just ordered a Velodyne DPS-12, which is front firing and I believe ported to the front. I haven't received it yet (just ordered it online yesterday) so I can't comment on how it sounds, but I've heard a lot of good things about Velodyne. I paid $340 + $50 S&H so it would fit well within your budget. Just an idea.
Scott, would you mind letting me know if the Velodyne is front ported once you receive it? I can audition Velodyne at a local retailer. Thanks for the idea.
Just got my sub yesterday. It's my very first, so my point of reference is nil, but it sounds great to me. I'm still trying to get everything configured the best way, but that has more to do with my receiver than anything... I'm very happy with the sub though and I think I got a great deal relative to other places I've seen it advertised.
The port is in front, along the bottom, just below the speaker itself. No other openings on the thing. Hope that helps.